U.S. lags in devising early quake warning

Sensors could give a 60-second advance notice

ALICIA CHANG, Associated Press

Published 5:30 am, Tuesday, May 30, 2006

PASADENA, CALIF. - The ground heaves, an earthquake is born. Underground sensors along fault lines detect rumblings humans can't and relay signals to a central computer. Precious seconds before anything is felt, wailing sirens blare that a big one is on its way.

That sliver of time could be used to warn people to flee from windows and take cover. Companies such as gas and electric utilities could take actions to protect their systems. And speeding trains could have enough time to brake to a halt.

Such alert systems already exist in parts of Japan, Mexico, Taiwan and Turkey, where the main users are businesses such as railway companies, power plants and manufacturers. But that's not the case in the United States — except for a handful of schools, firehouses and airports that use commercially available, battery-powered seismic gadgets that warn a limited region.

This summer, the U.S. Geological Survey is cautiously taking another look at early warning, beginning with a three-year test to gauge how well three experimental systems around California would work.

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Scientists will gather data without broadcasting alerts to residents or businesses. While a working system is still years and tens of millions of dollars away, many see the pilot project as a first step toward catching up with the rest of the world.

Many existing global networks sprang from killer quakes, and some scientists fear it would take a catastrophe to jolt the U.S. into action.

"If the capital of the United States were Los Angeles, we would have had an early warning system a long time ago," said Tom Heaton, professor of earthquake engineering at the California Institute of Technology and developer of one of the test systems.

Early warning systems can't predict quakes. Instead, a network of sensors near the epicenter estimates a temblor's size once the ground ruptures and sounds an alarm before shaking starts by exploiting the lag time it takes for different seismic waves to travel to the surface.

This is possible because shock waves coursing through the Earth move slower than electronic signals transmitted via a computer data network.

Weak tremors called primary waves, or P waves, spread from the epicenter and travel faster than the destructive shear waves, also called secondary or S waves, which cause severe shaking. The amount of forewarning depends on the distance from the epicenter, so early warning won't work for areas directly above the ruptured fault, where the P and S waves are nearly simultaneous and shaking is the most intense. According to some estimates, communities radiating miles from the deadly San Andreas fault could receive up to 60 seconds of warning.

Supporters say that gives communities a fighting chance to reduce injuries and damage. Skeptics contend seconds are hardly enough time to make a real difference.

"When people think of early warning, they think they'll get time to do something useful before shaking starts," said David Wald of the USGS National Earthquake Center in Colorado. "But in reality, you don't get a lot of time."

Japan pioneered seismic early warning in the 1980s with a system that automatically halted its high-speed trains during major quakes. Mexico, Taiwan and Turkey followed, though their alert systems are much less complex.

Early warning isn't foolproof: About 10 percent of the 245 warnings that the newest Japanese system sent between February 2004 and last August were false alarms.

Mexico's $2 million alert system, installed after the 1985 quake flattened much of Mexico City, was suspended twice during its inaugural year after a computer glitch failed to detect a major quake and a false alarm caused a subway stampede.